My city.

My city.

There is a supermarket along the main street. (We can use "along" to indicate the position of a building beside a road, river and so on. / If you are referring to "main street" as the name of a street, it has to be capitalised as it is a proper noun. If you are referring to the street as a major thoroughfare of your city, it does not need to be capitalised. However, you still need a specific determiner "the" because you are referring specifically to THAT main street.)

There is a Starbucks near the supermarket.

The ice cream shop is opposite side of the road of the supermarket.

(I eliminated your "side of the road of .." because your first sentence already indicates that the supermarket is located along one side of the main street / located along one side of Main Street. So, when you use "opposite", we can infer that the ice cream shop is on the other side or the road. The part "of the road of the supermarket" is erroneous. We often use the preposition "of" to indicate position or possession. The "opposite side" is part of the road indeed, but "road of the supermarket" sounds unnatural as the road is not part of the supermarket. 

If you still prefer to refer to the road, you may write: "The ice cream shop is across the road from the supermarket." In this new sentence, we use "from" to indicate your origin of travel -- your starting point is the supermarket; you cross the road to reach your ice cream shop.)


The fountain is at the centre of the roundabout. / The fountain is in the middle of the roundabout. 

As the fountain is within a middle area, we use "in" instead of "on". Hence, we can write: "The fountain is in the middle of the roundabout." 

Another possible way is to write "at the centre". In this case, we use "at" to refer to a very specific spot (centre). 

Hope this helps.

Cheers,

Lance